Investigation of space flight effects on Escherichia coli and a proposed model of underlying physical mechanisms

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Abstract
Previous investigations have reported that space flight may produce a stimulating effect on microbial metabolism; however, the specific underlying mechanisms associated with the observed changes have not yet been identified. In an effort to systematically evaluate the effect of space flight on each phase of microbial growth (lag, exponential and stationary), a series of experiments was carried out using in vitro suspension cultures of Escherichia coli aboard seven US Space Shuttle missions. The results indicated that, as a result of space flight, the lag phase was shortened, the duration of exponential growth was increased, and the final cell population density was approximately doubled. A model was derived from these cumulative data in an attempt to associate gravity-dependent, extracellular transport phenomena with unique changes observed in each specific phase of growth. It is suggested that a cumulative effect of gravity may have a significant impact on suspended cells via their fluid environment, where an immediate, direct influence of gravity might otherwise be deemed negligible.